1. Field of the Invention
The present invention generally relates to photolithographic processing for a mask layout and more particularly to an improved method which eliminates optical proximity effects such a rounding of corners and line end foreshortening etc. through an improved hierarchy and domain-balanced serif mask design system and method.
2. Description of the Related Art
Microlithography is the technology of reproducing patterns using light. As presently used in the semiconductor industry, a photomask pattern for a desired circuit is transferred to a wafer through light exposure, development, etch, and resist strip, etc. As feature sizes on a circuit become smaller and smaller, the circuit shape on the wafer differs from the original mask pattern more and more. In particular, corner rounding, line end foreshortening, iso-dense print bias, etc. are typically observed. These phenomena are called optical proximity effects.
One of the main reasons for optical proximity effects is light diffraction. Optical proximity effects coming from light diffraction can be overcome partly by using a shorter wavelength source of light, with a projection system possessing a larger numerical aperture. In practice, the wavelength of an optical light source is typically fixed (365 nm for i-line, 248 nm and 193 nm for DUV, 157 nm, etc.) and there is a practical upper limit on numerical aperture. So other resolution enhancement methods, including the use of phase-shifting masks and masks with serifs, have been developed to correct optical proximity effects.